Electrophotographic developers are a dry developer in which toner components composed of materials containing a colorant and a resin binder are used in a dry state, and a liquid developer in which toner components are dispersed in an insulating liquid.
In a liquid developer, toner particles are dispersed in oil in an insulating liquid, thereby making it possible to form smaller particle sizes as compared to a dry developer. Therefore, high-quality printouts can be obtained surpassing offset printing, so that the liquid developer is suitable for applications in commercial printings. In addition, in the recent years, since the demands for speeding up have been increasing, liquid developers in which toner particles having smaller particle sizes and reduced viscosities are stably dispersed therein have been desired. Also, a liquid developer in which toner particles are melt-fusable with a smaller amount of heat, in other words, a liquid developer having a low-temperature fusing ability, has been desired.
Patent Publication 1 discloses a method for producing a liquid developer utilizing a coacervation method, the method for producing a liquid developer characterized in that the method includes dispersing colored resin particles in an insulating hydrocarbon-based dispersion medium in the presence of a particle dispersant, which is a reaction product of a polyamine compound and a hydroxycarboxylic acid self-condensate, and an acidic group-containing resin.
Patent Publication 2 discloses a method for producing a liquid developer including the steps of adding a colored resin to a nonpolar dispersion medium, heating the nonpolar dispersion medium to a temperature of equal to or higher than a softening point of the resin, stirring the nonpolar dispersion medium to which the resin is added and heated to form a resin emulsion, and cooling the resin emulsion to solidify colored fine resin particles.
Patent Publication 3 discloses a method for producing a liquid developer in which toner particles are dispersed in an insulating liquid, characterized in that the method includes a molten mixture dispersion preparation step of preparing a molten mixture dispersion in which the kneaded mixture is finely dispersed in a molten state in the insulating liquid using a kneaded mixture containing a colorant and resin materials, and a cooling step of cooling the molten mixture dispersion to solidify the kneaded mixture in a molten state, wherein the insulating liquid is mainly composed of a non-volatile hydrocarbon.
Patent Publication 1: WO 2009/041634
Patent Publication 2: Japanese Patent Laid-Open No. Hei-09-179354
Patent Publication 3: Japanese Patent Laid-Open No. 2006-251253